Reinstating Pluto as a Planet

July 14, 2015

In "Is Pluto a Planet?" in the April 2015 issue of the Ohio Valley Parent Magazine, SMART Science discussed some ideas to talk to your friends and family about what is or is not a planet.

In August 2006 at a meeting of the International Astronomical Union, astronomers attempted to define the idea of what a planet is while demoting Pluto to a new category of smaller astronomical objects with the name dwarf planet. The IAU's definition of the idea of a planet is rather complicated, vague and did not speak to the many planet-sized objects being discovered beyond the Solar System. Few astronomers agreed with the new IAU planetary definition. Nine years later there is still much disagreement and debate on what is or is not a planet.

Pictured is the best image of Pluto so far from NASA's New Horizons spacecraft as of May 12, 2015 - stand by for high-definition images.

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In the absence of a better definition for what a planet is, the SMART-Center formed a working group several years ago to better define the term planet. This SMART-Center working group called the "BluePrint Team" is a citizen science group working toward creating an easy/simple definition of what a planet is.

Using more than eight years of research, attending and presenting at numerous astronomical conferences and educational workshops, and listening to the feedback from kids and adults at our co-sponsored StarWatches, the BluePrint Team has put forth a simple definition of a planet: A planet is a celestial object that is not massive enough to be a star and has a minimum diameter equal to 10 million "waves."

A wave is a new unit of length defined as the length of the wavelength of a universal radio frequency of hydrogen, the most abundant and simplest element in the universe. Hydrogen found in the space between the stars gives off a special radio wave called the hydrogen line. The length of the hydrogen line radio wave is 21.106 cm (8.309 inches). The symbol for this new unit of length is wv. By what the BluePrint Team calls a happy accident, "wv" is also the abbreviation for the state of West Virginia.

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Using this new definition of a planet, we can say that any object that is not a star and has a diameter equal to or larger than 10 MegaWaves (or 10 Mwv or 2,110.6 km or 1,311.7 miles) is defined as a planet.

This planetary definition is simple and straightforward, allowing no mistake when asking if a celestial object is a planet or not.

The current eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune are all much larger that 10 Mwv, so they continue to remain as planets by this new definition.

However, Pluto is a rather small celestial object.

Now, you may ask, where does Pluto fall according to the revised BluePrint Team's definition of a planet? The presently accepted diameter of Pluto is 2,322 km (1,443 miles) or about 11 Mwv.

Therefore, Pluto, by this new planetary definition, is just slightly larger than the minimum diameter of a planet, reinstating Pluto as a planet, a very small planet.

The New Horizons spacecraft will arrive and fly through the Pluto system on July 14.

In celebration visit www.smartcentermarket.com for news about Planet Pluto Camp (July 13-14) for fourth- to eighth-graders and the Planet Pluto Public Party and StarWatch from 6-9 p.m. July 14. Call 304-233-4667 for more information.

Visit the website, pluto.jhuapl.edu/, for updates, new Pluto images and data, and to watch the Pluto Flyby Countdown Clock.

Libby and Robert Strong and Richard Pollack work with the SMART-Center, a hands-on science outreach and education organization in the northern Ohio Valley, the headquarters of which is located at the SMART Centre Market, 30 22nd St., Wheeling.